Incidence of post-traumatic stress disorder is a major problem for the VA, affecting roughly 20% of individuals serving in OIF or OEF. Women appear to be more susceptible to development of PTSD than men, often occurring in the context of sexual assault (which can occur during military service). Frontline treatment options (e.g., SSRIs) can improve symptoms but do not currently offer a cure. To develop further strategies to this end, it is critical to understand the foundations of the disease process as it develops. This proposal is designed to examine the role of pituitary adenylate cyclase activating peptide, or PACAP, in mediating the development of aberrant physiological and behavioral fear responses following exposure to a chronic stress regimen. Recent studies indicate that polymorphisms in the primary PACAP receptor, PAC1, are linked to PTSD susceptibility in women. Preclinical data link deficits in PACAP to impaired emotional memory and blunted corticosterone stress responses, both of which accompany PTSD. Moreover, our preliminary studies suggest that chronic stress produces a profound and long-lasting deficit in PACAP expression in the prefrontal cortex, a region known to be dysfunctional in PTSD patients. These studies will use behavioral, physiological and genetic approaches to test the hypothesis that prefrontal cortex PACAP inhibits the development of PTSD-related physiological and behavioral deficits caused by chronic stress, identifying it as a potential therapeutic target. Aim 1 will test whether prefrontal PACAP signaling is necessary and sufficient to block the negative impact of chronic stress on behavioral and physiological indices of post-traumatic stress in rats. Endpoints tested include fear conditioning, extinction and extinction recall; fear generalization; anxiety-related behaviors; and hypothalamo-pituitary responses, all of which are disrupted following chronic stress (and in PTSD). Aim 2 will use prefrontal cortex-directed RNA interference and PACAP supplementation to test whether supplementation of PACAP during chronic stress can prevent the development of post-traumatic endpoints, or if loss of PACAP signaling is sufficient to induce aberrant emotional responses in otherwise unstressed animals. Aim 3 will test use electrophysiology and state-of-the-art imaging approaches to test the role of PACAP in mitigating potentially deleterious neuroplastic responses to chronic stress at the cellular level. In all cases, experiments will be performed in male and female subjects, to evaluate the possibility that females may be more sensitive to perturbations in PACAP signaling. These studies will provide important information regarding the prospect of using PACAP supplementation as a PTSD treatment, and determine whether females may be more likely to benefit from PACAP therapy.